1. Field of the Invention
The present invention relates to a semiconductor memory device, and more specifically, to a semiconductor memory device including a non-volatile memory element.
2. Description of the Related Art
In semiconductor memory devices, a non-volatile memory device is programmed in order to store data used for rescue of a defective memory cell, setting of an operation mode, etc. For example, in a redundancy circuit of a memory, a fuse element is used as a non-volatile memory element in order to store an address of a defective memory cell.
The fuse element made of, for example, a metal stores data (data “0” and data “1”) based on whether or not it is blown. As a system for programming the fuse element, the laser fuse system is mainly employed, in which the fuse element is vaporized with a laser beam to disconnect it. In order to reliably break (“blow”) a fuse element using the laser fuse system, it is necessary to apply a laser beam of a sufficient energy to the fuse element.
In recent years, as the density of the integration of the semiconductor memory device increases, the size of the transistor used in the semiconductor memory device is reduced. However, the semiconductor memory device that includes a transistor of a reduced size, entails the following drawback. That is, when the fuse element is blown with a laser beam, the transistor connected to the fuse element or the oxide film or diffusion layer of a transistor located near the fuse element are destroyed due to the energy of the disconnection of the fuse element. Thus, there might occur such a problem that a semiconductor memory device that comprises a nonvolatile memory element cannot realize the function as a ROM (read only memory).
As a related technique to the above-described conventional technique, there has been proposed a device that can program a fuse element with high energy (see Jpn. Pat. Appln. KOKAI Publication No. 2004-111959).